than those of the fundus and body. Those glands contain more mucous
cells and many gastrin-secreting enteroendocrine cells. Food entering the
pylorus stimulates the release of gastrin that stimulates HCl production by
the parietal cells. The pylorus connects with the duodenum (G),which
contains the mucus and bicarbonate-neutralizing secretion of the Brunner’s
glands. The wall of the stomach consists of the mucosa (epithelium, lamina
propria, and muscularis mucosa), submucosa, muscularis externa, and
serosa (B)lined by a mesothelium.
221.The answer is e. (Kasper, pp 755, 910–911. Kierszenbaum, pp
427–429. Alberts, pp 856, 1427–1428, 1437.)Cholera toxin causes secretory
diarrhea through the ADP-ribosylation of GSof the GTP-binding protein,
which leads to elevated cyclic AMP and the opening of the chloride chan-
nel(answers c & d).The exit of chloride through the open channels is fol-
lowed by the passage of sodium and water. The result can be dehydration,
which can be offset by intravenous feeding or oral rehydration therapy.
Pancreatic secretion is regulated by hormones. Secretin regulates ductal
secretion, whereas cholecystokinin (answer b)regulates the release of
enzymes (amylase, lipase, DNAse, RNAse, and the other enzymes that
compose the pancreatic juice). A number of pancreatic secretions are
released into the pancreatic duct system as zymogens (inactive precursors).
They are activated only when they arrive in the small intestinal lumen.
Enterokinase, a brush border enterocyte enzyme, converts trypsinogen to
trypsin (answer a).Trypsin and enterokinase are responsible for the acti-
vation of chymotrypsinogen, proelastase, and procarboxypeptidase A and
B to their active forms: chymotrypsin, elastase, and carboxypeptidase A
and B. These hormones are notrelated to cholera-induced diarrhea.
222.The answer is a.(Kierszenbaum, pp 427–429. Kumar, pp 844–845.
Kapser, pp 222–223.)The area shown in the photomicrograph is the glycoca-
lyx (brush border consisting of microvilli) of the small intestinal epithelium.
It is the location of the brush border enzymes including lactase. The patient
in the scenario is suffering from lactase deficiency which often has an adult
onset since lactase activity decreases after childhood. The absence of lactase
or reduced lactase activity results in passage of undigested lactose into the
colon. Colonic bacteria carry out fermentation of the lactose to organic
acids and hydrogen. The bloating, cramping, and abdominal pain are due
to the breakdown of lactose and production of the hydrogen gas. The
Gastrointestinal Tract and Glands Answers 339